The present invention relates to a gear-type stepless transmission mechanism usable for motive power machines in general.
A stepless transmission mechanism requires that the ratio of the rotation speed of the output shaft of the transmission mechnism to that of the input shaft thereof is zero. In other words, the ratio of the speed reduction from the input shaft to the output shaft is infinitely great for the range of continuous variableness of the stepless speed changing function of the transmission mechanism A rotation speed ratio for the output to input shafts of zero is a basic requirement and a very important art for performing the ideal control of the characteristic relationship between the angular velocity and shaft torque of the transmission mechanism in the use of the transmission mechanism for a motor vehicle. The use of the transmission is on condition that the motive power transmitted by the transmittion mechanism is substantially constant. A conventional art of such kind and a conventional stepless transmission mechanism based on the art were disclosed in the Japanese patent application (OPI) No. 72966/88 (the term "OPI" as used herein means an "unexamined published application") made by the present applicant. In the conventional stepless transmission mechanism, an elastic torsion member is provided so that preset elastic torque is applied to the member. The elastic torque and torque which is transmitted by the transmission mechanism interact to each other. The deflection angle of the elastic torsion member changes in correlation to the magnitude of the torque transmitted by the transmission mechanism. This relationship automatically regulates the ratio of the rotation speed of the output shaft of the transmission mechanism to that of the input shaft thereof.
The characteristic of the change in the rotation speed ratio of the conventional stepless transmission mechanism depends on that of the preset elastic torque applied to the elastic torsion member, so that stepless speed changing characteristic, which is controlled depending on the magnitude of the torque transmitted by the transmission mechanism, is created. FIG. 20 shows an example of the stepless speed changing characteristic of the conventional stepless transmission mechanism. It is understood from FIG. 20 that the ratio of the rotation speed of the output shaft to that of the input shaft at the time of driving a load which requires output torque of 2 kg.m is set at about -0.13, and input torque necessary for the driving can be calculated to be about 0.26 kg.m. It is a feature of the transmission mechanism that the ratio of the rotation speed of the output shaft to that of the input shaft is controlled depending on not the magnitude of the rotation speed of the transmission mechanism but that of the torque transmitted by the transmission mechanism. For that reason, the matchability of the transmission mechanism to various kinds of prime movers depends on the motive power generation characteristics of the prime movers. The matchability of the transmission mechanism to prime movers such as an external combustion engine, a person and a domestic animal, the torque generation characteristics of which do not depend on the rotation speeds of the prime movers, is high. The matchability of the transmission mechanism to other prime movers such as a D.C. motor with series excitation, for which it is easy to generate high torque in the low rotation speed range, is higher. On the other hand, the matchability of the transmission mechanism to yet other prime movers such as an induction motor and an internal combustion engine, in which very low torque is generated in the low rotation speed range but increases along with the rise in the rotation speed, is low. Since the characteristic of the preset elastic torque applied to the elastic torsion member is more related to the low torque generation side of the low rotation speed range anyway when each of the last-mentioned prime movers is used in a wide range of rotation speed in conjunction with the transmission mechanism, the transmission mechanism is likely to have such a control characteristic as to render it difficult to make full use of the motive power of the prime mover in the high rotation speed range. This is the problem.